Before his death in 1609, the brilliant Elizabethan spy, astrologer and mathematician John Dee hid many of his papers, believing that the world was not prepared for the ideas they held. For seventeen generations, his female descendants have held his most precious secrets, waiting for the right moment to bring them to light.

In spring 2003, Dee's many times great granddaughter, dying of cancer, was forced to pass the enigmatic legacy to one of her two sons. Diana chose her passionate, tempestuous younger boy, leaving a tiny silver key and a piece of parchment with a note: For Will, when he is something, or someone, that he is not now.

Over the long, hot summer of 2003, while seriously ill Lucy King awaits heart surgery in London, Will travels Europe seeking to decipher the clues in the ancient document, and find a lock to fit the key. It is a search that will leave him and Lucy inextricably linked, and lead into a world of extraordinary riddles and dangerous secrets.